President Biden intends to use a prime-time address near Philadelphia’s Independence Hall to lay out what he views as the stakes for the nation’s democracy at a time when millions of Americans have questioned the legitimacy of the 2020 presidential election.

Mr. Biden’s speech Thursday will come just ahead of the traditional Labor Day start of the midterm-election campaign season and will focus on values such as equality and democracy, which he is expected to describe as part of a continuing “battle for the soul of the nation,” according to a senior White House official.